Earth-Abundant Divalent Cation High-Entropy Spinel Ferrites as Bifunctional Electrocatalysts for Oxygen Evolution and Reduction Reactions

High-entropy spinel ferrites (HESFs) offer long-term stability and activity in oxygen electrochemical reactions due to entropy stabilization and synergistic effects of multiple elements within their crystal structure. However, conventional HESFs often rely on transition metals for high configurational entropy, limiting their accessibility and sustainability. In this study, we successfully synthesized a high-entropy spinel oxide using earth-abundant elements, such as Mg, Cu, and Zn (Mg-Fe2O4), addressing the need for more sustainable materials without compromising performance. Despite differences in cation composition, both synthesized HESFs maintain identical crystal structures and lattice constants. Incorporating smaller-radius elements like Mg, Cu, and Zn does not affect the crystal structure, achieving high-entropy spinel ferrites with similar properties to traditional counterparts, e.g., (CoCrFeMnNi)Fe2O4. Material characterization and electrochemical analyses demonstrate comparable performance, including over 200 h of continuous battery operation. These findings highlight the potential of utilizing more accessible materials to create efficient HESFs, expanding their applicability in energy conversion and storage.